1. Field of the Invention
The present invention relates to a method for easily and efficiently forming a pattern of a non-volatile, high-performance ferroelectric thin film memory.
2. Description of the Prior Art
As a conventional method for patterning a ferroelectric film, a dry etching technique (Japanese Patent Provisional Publication No. 5-175,174) is available. This method comprises first forming a ferroelectric film on a substrate, forming an inorganic film thereon, forming an organic resist film by ordinary photolithography, then subjecting the thus formed resist film to exposure and development to form a resist mask, forming a mask pattern comprising an inorganic film by removing portions of the inorganic film by reactive ion etching, then removing the resist mask through an ashing treatment with an oxygen plasma, etching the metal film by dry etching with a halogen gas, and finally removing, as required, the mask pattern of the remaining inorganic film.
A method has also been proposed which comprises generating an acid by light irradiation with the use of an acid generating agent such as a sulfonic ester in a sol-gel solution of a ferroelectric substance and patterning a film of the solution using a polycondensation reaction (Japanese Patent Provisional Publication No. 5-116,454).
Of the conventional methods described above, the method based on dry etching has problems in that many steps including application of a resist, ion implantation and etching result in a high cost and it is difficult to handle the strong acid used for etching.
In the method using an acid generating agent, on the other hand, which permits patterning using a simple process, when using a sulfur-containing compound such as a sulfonic ester as an acid generating agent, sulfur from the acid generating agent remains in the resultant ferroelectric film and impairs the properties of the produced memory. The method using an acid generating agent in which the generated acid accelerates a polycondensation reaction, is defective in that the polycondensation reaction is lower with respect to reaction rate as compared with a hydrolysis reaction. This leads to low reaction efficiency.
The present invention has as an object, solving of the above-mentioned problems of the conventional methods and providing of a method for easily and efficiently forming a pattern of a nonvolatile, high-performance ferroelectric thin film memory.